The intestinal epithelium is sustained by a highly dynamic balance of cell proliferation, differentiation and senescence. Coordination of these processes is essential to functional and anatomic integrity. The overall goal of the studies described in this proposal is the delineation of the role of peptide growth factors in modulating proliferation and differentiation of intestinal epithelial cells at a molecular level. A major thrust of these efforts will be the examination of the regulation of expression of transforming growth factors alpha and beta (TGF alpha and beta) by intestinal epithelial cells and their role in effecting interactions between these cell populations and their extracellular matrix. Toward this goal the molecular basis of TGF regulation of a model cell surface receptor designated EGP which is involved in cell-matrix adherence will be defined through transient transfection assays in established intestinal epithelial cell lines. These studies will serve as a paradigm to understand the role of the cell surface receptors and cell matrix components in growth modulation by these peptide growth factors. In addition to a detailed examination of the role of previously recognized peptide growth factors, important goals will be the molecular characterization of two novel and biologically complementary proteins with potent growth regulating activity which are expressed by intestinal epithelial cells: MER-TGF, a protein first purified from malignant effusion which has been found by cDNA cloning to have homology to the proto-oncogene wnt-1, and TGIF, a protein which inhibits anchorage independent growth of colon-carcinoma derived cell lines and appears to have significant homology to the c-fms proto-oncogene encoding the receptor for CSF-1, a protein regulating hematopoietic stem cells. Efforts will be directed to the completion of molecular cloning of these factors as well as biochemical and biological characterization of the encoded transcripts. Regulatory elements will be defined in parallel with characterization of their effects on established intestinal epithelial cell lines and primary enterocytes. The inter-relationship between both expression and cellular response to these factors and the ubiquitous TGFs will be delineated. The relevance of the spectrum of peptide growth factors identified and characterized in a number of intestinal epithelial cell lines will be explored in the intact intestinal mucosa. The importance of this integrated network in sustaining mucosal integrity will be defined through an in vitro model of epithelial wounding as well as in vivo models of mucosal injury in the intact animal. In aggregate, these studies will provide insight into the spectrum of factors and the mechanisms which play a role in maintaining mucosal epithelial homeostasis. These insights are intrinsic to understanding injury and healing in inflammatory bowel disease and other diseases.